point camera to empty
The second line with "X Y Z" of the "direction to rotation" node is to indicate which axis of the object is to keep to the direction indicated in the "guide" vector in the bottom part of the node.

Here we have Z=1 (up) as guide so using Y will align to Z.

A complement: using this guide you can also plug the target's rotation as guide. This will give the following effect (note that AN is clever enough to automatically convert the rotation as a direction, adding another "rotation to direction" node):